Trejos A.,Metropolitan Institute of Technology |
Gonzalez D.,National University of Colombia |
Ramos-Paja C.A.,National University of Colombia
Energies | Year: 2012
This paper presents modeling approaches for step-up grid-connected photovoltaic systems intended to provide analytical tools for control design. The first approach is based on a voltage source representation of the bulk capacitor interacting with the grid-connected inverter, which is a common model for large DC buses and closed-loop inverters. The second approach considers the inverter of a double-stage PV system as a Norton equivalent, which is widely accepted for open-loop inverters. In addition, the paper considers both ideal and realistic models for the DC/DC converter that interacts with the PV module, providing four mathematical models to cover a wide range of applications. The models are expressed in state space representation to simplify its use in analysis and control design, and also to be easily implemented in simulation software, e.g., Matlab. The PV system was analyzed to demonstrate the non-minimum phase condition for all the models, which is an important aspect to select the control technique. Moreover, the system observability and controllability were studied to define design criteria. Finally, the analytical results are illustrated by means of detailed simulations, and the paper results are validated in an experimental test bench. © 2012 by the authors.
Dario Gomez N.,Metropolitan Institute of Technology |
Gomez J.A.,Jaime Isaza Cadavid Colombian Polytechnic
Optics and Lasers in Engineering | Year: 2013
In this work, a technique to improve the dynamical behavior of a non holographic fiber specklegram sensor for measuring high frequency mechanical perturbations is experimentally demonstrated. In these arrangements, the speckle pattern produced by a multimode optical fiber is coupled to an optical fiber of low numerical aperture, which produces a filtering effect that can be used as optical transduction mechanism. In our proposal, the influence of the speckle size on the sensor performance is evaluated by changes in the numerical aperture of the multimode fiber. A strong effect of the near field fiber speckle size on the reproducibility of the mechanical perturbation is found. The behavior of the reproducibility is evaluated by the calculation of the mean of the variance and the correlation between the mechanical and optical normalized signals. © 2013 Elsevier Ltd.
Xu J.,University of Tokyo |
Kawaguchi M.,Metropolitan Institute of Technology |
Kato T.,University of Tokyo
Tribology International | Year: 2014
The evolution of transfer layers derived from a-C:H coating/steel ball tribopairs sliding in ambient air is tracked by performing one set of overlapping tribotests on a ball-on-plate device with acceptable repeatability of friction coefficients. After sliding tests, counterparts were separated and probed by optical microscopy, SEM/EDX and XPS. Carbon-based transfer layers were built up in the first cycle of sliding. Except for the typical graphitization of transferred carbon materials, a chemisorbed layer rich in C/O groups was also found on the top surface of transfer layers, and considerably affected the friction behavior of a-C:H coating/steel tribopairs in ambient air. © 2013 Elsevier Ltd.
Ponce W.A.,University of Antioquia |
Benavides R.H.,University of Antioquia |
Benavides R.H.,Metropolitan Institute of Technology
European Physical Journal C | Year: 2011
A way of counting free parameters in the quark mass matrices of the standard model, including the constraints coming from weak basis transformations, is presented; this allows one to understand the exact physical meaning of the parallel and non-parallel texture zeros which appear in some “ansätze” of the 3 × 3 quark mass matrices, including the CP violation phenomena in the analysis; it is shown why the six texture zeros are ruled out. Finally, a five texture zeros “ansatz” which properly copes with all experimental constrains, including the angles of the unitary triangle, is presented. 00A9; Springer-Verlag / Società Italiana di Fisica 2011.
Ponce W.A.,University of Antioquia |
Gomez J.D.,University of Antioquia |
Benavides R.H.,Metropolitan Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
The phenomenology of the five independent sets of 3×3 quark mass matrices with five texture zeros is carried through in full detail, including predictions for the CP-violation asymmetries. Our study is done without any approximation, first analytically and then numerically. © 2013 American Physical Society.
Pastor-Perez L.,University of Alicante |
Buitrago-Sierra R.,Metropolitan Institute of Technology |
Sepulveda-Escribano A.,University of Alicante
International Journal of Hydrogen Energy | Year: 2014
The low temperature water-gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as references. A combination of N2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H2, X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni-CeO2 interactions and the CeO2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H2O) and a slightly harder one (with CO, CO2, H2, and H2O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO2 and H2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO2, and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction. © 2014 Hydrogen Energy Publications, LLC.
A heterodox perspective on the history of drugs. Inclusion-exclusion dynamics of the Ravetllat-Pla anti-tuberculosis serum in the first third of the 20th century [Una perspectiva heterodoxa de la historia de los medicamentos. Dinámicas de inclusión-exclusión de los sueros antituberculosos Ravetllat-Pla en la España del primer tercio del siglo XX]
Lugo-Marquez S.,Metropolitan Institute of Technology
Dynamis | Year: 2013
In 1924, a historically peak time for tuberculosis in Spain, the Ravetllat-Pla Institute was established with the aim of producing and commercializing an anti-tuberculosis serum and researching the variability of the bacteria implicated in this infection. This bacterial form, proposed by Joaquim Ravetllat in the first decade of the 20th century, led to the formulation of a new etiological-pathologic theory of tuberculosis, which upheld the drugs produced by the Institute and was considered heterodox by the official science of the time. The Catalan medical and political network established a space of exclusion leading to the marginalization of the Institute, which, by strengthening its heterodox identity, generated another space of inclusion. In this space, its refuted scientific theory could be socially legitimated and validated through the commercial success of its pharmaceutical products. In this paper, we suggest that the consideration of medicines as commercial products illustrates the active participation of the different users of the Ravetllat-Pla serum in its social construction, re-conceptualization and legitimization. Moreover, from the theoretical framework of inclusion-exclusion dynamics, this research contributes to understanding the processes of knowledge legitimatization by scientific heterodoxy. © 2013, Editorial Universida de Granada. All rights reserved.
Serna E.M.,Metropolitan Institute of Technology
International Journal of Information Management | Year: 2015
Abstract In this article a maturity model for the management of transdisciplinary knowledge is presented, although research nowadays is transdisciplinary the different maturity models proposed in the literature are oriented towards interdisciplinary knowledge management, and, at most, they are oriented toward multidisciplinary knowledge management. The objective is proposing an evolutionary model which accepts knowledge as intensely active and dynamic and evolving in maturity from the early stages of research. But this is possible only if the research team adopt a clear, clean and joint process of disciplinary integration and transdisciplinary integration of the produced and discovered knowledge. In this way, the results of research will have a greater influence on society and they also will be adopted by society. © 2015 Elsevier Ltd.
Roldan-Vasco S.,Metropolitan Institute of Technology
2014 19th Symposium on Image, Signal Processing and Artificial Vision, STSIVA 2014 | Year: 2015
The Deep Brain Stimulation is a surgical procedure in which an electrode is implanted, used by functional neurosurgeons to control the discharge rates of motor units (basal ganglia) in patients with movement disorders. The success of the procedure depends on exactly localization of surgical target, conventionally the subthalamic nucleus, thalamus or globus pallidus internus, which have a particular voltage profile. In this work, two kind of parametric structures, non-linear ARX and linear AR, have been used for modeling the intracerebral signals in patients with Parkinson disease. This work evaluates the fitness with both modeling techniques and their dependence of the linearity regressors and the prediction horizon. The author found that the signals without Gaussian behavior were strongly sensitive of the prediction horizon. On the other hand, both AR and NLARX had good enough precision that guarantees an accurate simulation. This work aims to establish the better modeling criteria trough an a comparison between fitness for AR and NLARX structures and the final model of subthalamic nucleus signals for an oblique coordinate system. © 2014 IEEE.
Pedroza-Diaz J.,Metropolitan Institute of Technology |
Rothlisberger S.,Metropolitan Institute of Technology
Biochemia Medica | Year: 2015
The discovery of protein biomarkers that reflect the biological state of the body is of vital importance to disease management.Urine is an ideal source of biomarkers that provides a non-invasive approach to diagnosis, prognosis and prediction of diseases.Consequently, the study of the human urinary proteome has increased dramatically over the last 10 years, with many studies being published.This review focuses on urinary protein biomarkers that have shown potential, in initial studies, for diseases affecting the urogenital tract, specifically chronic kidney disease and prostate cancer, as well as other non-urogenital pathologies such as breast cancer, diabetes, atherosclerosis and osteoarthritis.PubMed was searched for peer-reviewed literature on the subject, published in the last 10 years.The keywords used were “urine, biomarker, protein, and/or prostate cancer/ breast cancer/chronic kidney disease/diabetes/atherosclerosis/osteoarthritis”.Original studies on the subject, as well as a small number of reviews, were analysed including the strengths and weaknesses, and we summarized the performance of biomarkers that demonstrated potential.One of the biggest challenges found is that biomarkers are often shared by several pathologies so are not specific to one disease.Therefore, the trend is shifting towards implementing a panel of biomarkers, which may increase specificity.Although there have been many advances in urinary proteomics, these have not resulted in similar advancements in clinical practice due to high costs and the lack of large data sets.In order to translate these potential biomarkers to clinical practice, vigorous validation is needed, with input from industry or large collaborative studies. © by Croatian Society of Medical Biochemistry and Laboratory Medicine.